The strongest oxidizing agent suitable for soil and groundwater remediation is the hydroxyl free radical. The typical way to generate OH radicals is through the Fenton system using H2O2 and ferrous ions at pH 3-4. Hydroxyl free radicals can also be generated by the use of a combination of ozone and H2O2 or UV and H2O2.
While these technologies are effective, they suffer from some drawbacks:                Fenton technology is only suitable at a low pH, hence the need to acidify which requires the use of stainless steel piping and is expensive.        Ozone/H2O2 technology requires on site generation of ozone and can be expensive.        UV/H2O2 technology is not suitable for in-situ remediation.        
Hydrogen peroxide solutions are available in several concentrations. The typical concentration used in soil remediation is the 35% grade. This is further diluted to lower concentrations for example 5-12%, before introduction in the contaminated material to be treated.
Sodium percarbonate (PCS) is a peroxyhydrate composed of sodium carbonate and H2O2. Its solubility in water is ˜12%. Upon dissolution in water, it releases its components and the resulting solution contains both soda ash and H2O2.
Calcium and magnesium peroxide are solid peroxygens that are insoluble in water. When they are mixed with water, they slowly release oxygen at their natural pH (>pH 10). They are used in soil and groundwater remediation to provide oxygen to aerobic bacteria thereby enhancing their capability of degrading various contaminants.
As the pH is lowered, CaO2 and MgO2 generate increasingly larger quantities of H2O2. For example, at a pH 8, approximately 60% of the active content of CaO2 can be generated in the form of H2O2.
Whereas OH radicals can be generated at any pH due to H2O2 decomposition, the optimal use of this process for chemical oxidation occurs at a pH of 3-4 whereby the Fe ions remain soluble, and cycle between a ferrous and a ferric state.
U.S. Pat. No. 6,268,205 discusses the use of inorganic peroxides in conjunction with buffers and catalyst such as ferrous or ferric sulfate. The pH of such system is adjusted to 7-9. Under these conditions, the metal peroxides will release their activity partially as H2O2 and partially as oxygen. This allows for the initial chemical oxidation to take place starting the break up of the contaminants. The oxygen is then released more slowly, which will assist bioremediation over a period of several months. Although OH radicals can be generated from H2O2 at this pH, Fe will precipitate as ferric hydroxide. The net result is a reduced generation of OH radicals and clogging of the medium with the precipitated ferric hydroxide.
U.S. Pat. Nos. 5,741,427 and 6,319,328 are related to the use of Fe salts or chelates that are dissolved in water, the solution is maintained at pH 5-8, and then injected to a soil that has already been injected with an oxidizing agent. This pH is lower than the pH claimed in the above patent and would lead to a very fast release of H2O2 from the solid peroxides. The order of addition claimed results in a reduced activation of H2O2 as the peroxide would be partially decomposed prior to the injection of the metal chelate.
U.S. Pat. No. 6,843,618 is related to a method of decontaminating soil and ground water containing organic contaminants and divalent metal compounds. It comprises the steps of first treating such soils and ground water with an effective amount of an aqueous solution containing a peroxide and a water soluble chelating agent for a time sufficient to have the water soluble chelating agent chelate at least one of the divalent metals of the divalent metal compounds present in the soil and ground water. Next, the chelated metals are brought into contact with the peroxide to catalytically convert the peroxide to an oxidizing agent. Finally, the last step is contacting the organic contaminants in the soil and ground water with the oxidizing agent to oxidize the organic contaminants to environmentally safe, non-toxic compounds.